One goal of loudspeaker systems is to achieve a low resonant frequency in a speaker enclosure that has a relatively small internal volume. The resonant frequency of a speaker enclosure can be decreased by adding an air adsorber to the enclosure; the adsorber acts to increase air compliance of the enclosure.
A good adsorption material should have at least the following characteristics. The amount of gas adsorbed and desorbed should be strongly dependent on the pressure change. Also, the adsorption properties of the material should not degrade or change significantly when exposed to different environmental conditions. Further, since the amount of space inside the speaker cabinet that can be devoted to air-adsorbing materials is limited, the material needs to be packaged such that it occupies a small volume. On the other hand, the amount of air adsorption is directly related to the amount of air-adsorbing material in the speaker enclosure. Also, the material must be packaged in a manner that allows air to reach it in acoustic applications, which generally need to be above 40 Hz.
Moisture in the atmosphere can be detrimental to the proper function of adsorption materials. Often when an adsorption material is exposed to a humid environment many adsorption sites are preferentially occupied by water molecules, leaving few sites for the adsorption/desorption of air molecules. This phenomenon renders the adsorption material ineffective in regulating the pressure of an acoustic enclosure through adsorption/desorption of air inside the enclosure.